Metal orbitals, exchanged electron

Percentage of "Exchanged Electron" Residing in Metal (M) and Ligand (L) Orbitals... 

The relative sizes of the polarization and delocalization mechanisms will depend on the orbitals involved in the overlap and the occupancies of the metal orbitals. For example, the polarization mechanism appears to be relatively weak for Ni. in contrast to Mn + and Cr +. even when both mechanisms involve eg orbitals. This is most likely due to the smaller exchange interaction expected for the Ni + system, which contains fewer unpaired electrons. Some earlier studies neglected the polarization mechanism, assuming that it was much weaker than the other possible shift mechanisms, which lead to incorrect assignments. ... 

The complex [(VO)2(dana)2] (dana = l,5-bis(p-methoxyphenyl)-l,3,5-pentanetrionato) was prepared and temperature dependent Xm measurements show antiferromagnetic behaviour with J = —80 cm 1.902 The / value is much lower than with [M2(dana)2(py)2] (M = Co, Cu) and this probably results from a different spatial orientation of the exchanging electrons if the unpaired electron is considered to be initially in a dxy orbital, a direct metal-metal interaction may be possible as the V—V distance is large (ca. 3.0-3.2 A V atoms are probably 0.5-0.6 A out of the plane and possibly one above and one below the ligand plane902), one would expect a weak exchange for the direct V—V interaction. 

A number of transition metal ion-exchange zeolites are active for acetylene trimerization (159, 160), and the criterion for activity appears to be an even, partially filled d-orbital, i.e., d8 (Ni2 +, Co+), d( (Fe2+), d4 (Cr2 + ). This has led to the suggestion that the mechanism must involve a complex in which there is simultaneous coordination of two acetylene molecules to the transition metal ion. The active oxidation state for CuNaY butadiene cyclodimerization catalysts has been unambiguously defined as monovalent copper (172-180). The d10 electronic configuration of Cu+ is consistent with the fact that isoelectronic complexes of Ni° and Pd° are active homogeneous catalysts for this reaction. The almost quantitative cyclodimerization selec-... 

The electronic states on the metal are labeled by their quasi-momentum k they can exchange electrons with the adsorbate orbital the corresponding terms are ... 

Fio. 7. The exchange of electron pairs between the metal orbitals and trans-... 

Oxidation-reduction reactions of transition-metal complexes involve electron transfer from one complex to another. The two molecules may be connected by a common ligand through which the electron is transferred (inner-sphere reaction), or the exchange may occur between two separate coordination spheres (outer-sphere reaction). Electron transfer rates depend on the rate of ligand substitution within the reactants, the match of the reactant orbital energies, solvation of reactants, and the nature of the ligands. These reactions have... 

M-O-Li, so that the spin transferred from the metal to the lithium ion is ahgned with the external magnetic field. The spin polarization mechanism relies on the quantum mechanical effect known as the exchange interaction, which causes unpaired electrons in a metal orbital to polarize the electrons in the other doubly occupied 3d orbitals. Thus an electron with the same spin as the unpaired electron in a second nonequivalent transition metal orbital is present at the metal site rather than an electron with the opposite spin. Positive spin density increases on the transition metal site while negative spin density is transferred to the oxygen and lithium orbitals. 

In the same way, there is exchange repulsion of lone pair orbitals on adsorbates and the occupied conduction electron levels in a metal. This effect is more important if the conduction electron density is higher. It has been pointed out by Post and Baerends [41] that the much higher conduction electron density of A1 (3 valence electrons) compared to Li (1 valence electron) leads to much stronger 5(j/metal-sp exchange repulsion with CO for A1 than Li. Bagus et al. [30] have stressed this (x-repulsion for CO interacting with metals. 

The most important effect of the configuration change from (4s+4s) doubly occupied to (4s—4s) doubly occupied is the disappearance of the 4-electron destabilizing interaction (exchange or Pauli repulsion) of the 5g (carbon lone pair) orbital of CO with the (4s + 4s) metal orbital. 

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